I have pressure like pain in my lower stomach during sex and have nausea after. !

I have pressure like pain in my lower stomach during sex and have nausea after. Also I have burning when I pee

I've never had normal periods. I have a 21 month old. I had the Iud until 2 months ago. Since I don't have a period, I don't know if I miss it or if I'm late. I've taken a cheap pregnancy test and it said negative. I have pressure like pain in my lower stomach during sex and have nausea afterwords. It also burns when I go to the bathroom after sex. I have cramps in my legs and lower back. I'm worried this could be something other than pregnancy. Anyone else had these problems before? Any ideas of what it could be?

It could be an infection, I would go to the doctor as soon as possible. They can do blood work to see if you are pregnant though and also they can check if there is any infection in your urine.